1. Technical Field
The present invention relates generally to a method and apparatus for measuring the synthetic reception pattern of an adaptive array antenna and, more particularly, to a method and apparatus that measure and evaluate information about a null depth, a null width, and a satellite blind ratio, which are the principal performance indices of an adaptive array antenna system, for respective component steps (antenna elements, radio frequency (RF) module, and signal processing module) of the array antenna system in anti jamming nulling technology using an array antenna which is one of effective methods for protecting a Global Navigation Satellite System (GNSS) receiver from GNSS interference signals.
2. Description of the Related Art
A Global Navigation Satellite System (GNSS), of which a Global Positioning System (GPS) is representative, denotes a satellite-based navigation system for receiving information about the location, time, and additional error correction elements of a satellite from the satellite, and acquiring the exact time and location information of a user. Currently, a GNSS is being variously utilized in ground, maritime, and air systems in both military and civil domains.
Since a GNSS satellite transmits a low power signal from a remote place located at a distance of 20,000 km or more, power received by a receiver is as weak as 10−16 W. Therefore, a GNSS system is inevitably inherently vulnerable to unintentional electromagnetic interference such as multi-path interference, or intentional electromagnetic jamming. If the GNSS, which is variously utilized as the core of social infrastructures such as various types of communication, broadcasting, financial and logistics applications, is jammed, it is expected that a serious problem causing social disorder would occur.
In this way, various types of technologies have been used to cope with jamming or radio interference that becomes a serious threat to the GNSS. Among these technologies, spatial filtering technology (referred to as “nulling”) using an array antenna is widely known as the most effective anti-jamming method. Here, nulling technology uses a principle in which multiple antennas are spatially arranged, and in which a signal is increased in a desired direction and an undesirable jamming signal is decreased by using a method of multiplying complex weights (or weight vectors) by the respective outputs of the antennas. Methods of implementing the same principle may be divided into an analog type and a digital type.
Recently, a digital array antenna system has been widely used in which signals received from antenna elements are converted into Intermediate Frequency (IF) signals via a down-converter, the IF signals are converted into digital signals at low frequency, and then anti jamming signal processing is performed on the digital signals via a digital signal processor with an adaptive nulling algorithm.
The performance indices of the anti jamming system using an adaptive array antenna may be chiefly divided into {circle around (1)} null depth, {circle around (2)} null width, and {circle around (3)} satellite blind ratio; all of which can be obtained from the synthetic reception pattern of the array antenna. A brief description of the individual performance indices is made as follows.
{circle around (1)} Null depth—index indicating the decrease in an undesired jamming signal, which is obtained via adaptive nulling processing.
{circle around (2)} Null width—index indicating the degree of attenuation of signals around a jamming direction caused by the side effect of adaptive filtering. This index is evaluated as the beamwidth at which signal intensity relative to an omni-directional antenna is reduced to ½ (−3 dB in power unit).
{circle around (3)} Satellite blind ratio—index indicating the reduction ratio of the number of GNSS visible satellites occurring when adaptive nulling processing is applied. This index indicates the ratio of the size of a satellite signal receivable area upon using an adaptive array antenna to the size of a satellite signal receivable area upon using an omni-directional antenna, and varies according to the performance of a receiver used.
However, since the above three performance indices of the adaptive array antenna system adaptively vary with the number, intensity, direction, and signal type of jamming signals, it is impossible to exactly measure such performance indices using traditional performance measurement methods related to an existing fixed reception pattern antenna (FRPA).
In outdoor test facilities having well-calibrated characteristics, some parameters may be measured, but there is a disadvantage in that tests preparation and calibration are time-consuming, and it is difficult to secure repeatability which is a precondition to the evaluation of performance. Further, in order to solve the problem of repeatability, measurement may be conducted in an anechoic chamber, but a problem arises in that an expensive multi-channel satellite simulator must be provided, and a lot of measurement time is required.
Therefore, there is required an injection test method using a simulator capable of reducing cost and measurement effort while securing repeatability.
As related preceding technology, Korean Patent Application Publication No. 10-2010-0081590 (entitled “Wavefront simulator for testing GPS adaptive array antenna”) discloses technology for randomly generating the wavefront of a GPS jamming signal incident on an array antenna so that performance can be evaluated in a laboratory other than an anechoic chamber and an outdoor test facility.
The invention disclosed in Korean Patent Application Publication No. 10-2010-0081590 is disadvantageous in that it is impossible to measure the synthetic reception pattern of an array antenna system, and thus only a null depth in a specific jamming direction can be detected, and additional performance indices such as a null width and a satellite blind ratio cannot be evaluated.
Further, the invention disclosed in Korean Patent Application Publication No. 10-2010-0081590 cannot evaluate the above performance indices for each of antenna elements, an RF module, and a signal processing module constituting the array antenna system. The evaluation of performance for each step of the components is very important to the analysis of limits and limiting factors for the entire system performance upon developing an anti jamming array antenna system.